European patent EP 0768308 B1 discloses mixtures of stereoisomers of pyroglutamic acid derivatives having the following general formula
wherein R1, R2 and R3 may be hydrogen or —C(═O)Me and A may be Cl—, CH3COO— or HO— to stimulate immune biological response. The process disclosed therein for the synthesis of said compounds comprises reacting L-serine with a molar excess of acetic anhydride and pyridine under heat. Therefore, as disclosed in said document, the different stereoisomers have never been isolated and the in vivo and in vitro assays disclosed therein are performed with the mixtures of the four possible optically active stereoisomers all together. No indication regarding pure or enriched mixtures of the individual stereoisomers is disclosed. Further, no indication regarding the isolation of the different optically active stereoisomers from the mixture disclosed is given.
It is known to the skilled person that the different optically active stereoisomers of a compound may have different, or even opposite, effects. For example, a compound may have therapeutic effects while its enantiomer may be toxic. Examples of such situations are well known to the skilled person. Dextromethorphan is a decongestant, while levomethorphan is a potent narcotic.

It is also known the different in vivo behaviour of the enantiomers of Perhexyline.

They are both modulators of cardiac rhythm, but one of the enantiomers is methanolised more slowly and accumulates in the body, situation which caused a number of deaths during 80's.
Probably the most tragic and well known example is thalidomide, which was administered as a racemic mixture to pregnant women in order to treat mourning sickness.

While R-thalidomide was effective, the teratogenic effects of S-thalidomide where later discovered.
Therefore, in the search for new compounds with beneficial therapeutic effects it is usually necessary to perform assays with the enantiomerically pure stereoisomers in an attempt to select the most active enantiomers and/or to discard the eventual toxic ones. Thus, there is a need to provide isolated stereoisomers of pyroglutamic acid derivatives.